General cameras (imaging devices) include viewfinders (display devices) for checking the composition and focus of captured images in real time. It is required with respect to captured images displayed on viewfinders to fully reproduce the angles of view and resolution of the images depending on purposes thereof. However, there are many cases, for example, in which viewfinders with HD resolution or the like which is lower than the resolution of captured images are used in high-resolution imaging devices (e.g., 4K cameras) for the reason of convenience in handling and installation.
The present applicant has proposed a technology for displaying edge information of a high-resolution image on a low-resolution display device before (refer to Patent Literature 1). This technology intends to enable focusing to be checked from edge information of a higher frequency band than a Nyquist frequency of low resolution by down-converting high frequency edge information, which is obtained by performing a filtering process on a high-resolution image, and displaying the edge information on the low-resolution display device.